The present invention relates to semiconductor integrated circuitry in which such circuit programming as circuit creation, circuit conversion and circuit substitution is possible and the utilization thereof, and a circuit programming system and method of such of a programmable integrated circuitry. More particularly, semiconductor integrated circuitry according to the present invention has a programming element incorporated in the circuit interconnection, and a circuit programming system and method according to the present invention is effected by means of the programming element.
As is well known, circuit programming for a semiconductor chip including therein an integrated circuit is carried out by cutting open a part of the circuit interconnection.
Such circuit programming has hitherto been used in, for example, the programming of a read-only memory (ROM). In recent years, it has been utilized in substituting a small number of spare memory elements for defective elements. The conventional approach for cutting open the circuit interconnection usually includes (1) the fusing of a fuse element by a current or (2) the application of external optical energy (a pulse laser beam).
FIGS. 1A and 1B of the accompanying drawings illustrate a conventional circuit programming method in which a polycrystalline silicon layer or an Al layer 1 electrically isolated from a silicon substrate 3 by an SiO.sub.2 film 2 formed thereon, is irradiated with a laser beam 4 to cut open the layer 1. As one example of this method, R. P. Cenker et al., 1979 ISSCC Digest of Technical Papers have reported their experimental results in which the interconnection with respect to decoders of an MOS memory is changed so as to disconnect a decoder connected to a defective memory cell and to replace the defective cell by a non-defective memory cell connected to a spare decoder.
However, the above method in which an element is cut open, has the following drawbacks. (1) A laser beam of high energy is required so that the molten polycrystalline silicon or aluminum damages a part of the SiO.sub.2 film adjacent thereto or the laser beam is apt to impair the substrate. Accordingly, a semiconductor chip is required to have much room for layout, which results in large-area chip. (2) The use of only the cutting approach for circuit programming is sometimes disadvantageous from the standpoint of effective utilization of chip area.